A component of nearly all modern day inkjet printers is an ink tank that delivers ink to the printhead in order to render a printed image. The ink tank prevents leakage of the ink during manufacture, storage, transportation, and the printing operation itself. In particular, once the ink tank is in fluidic communication with the printhead, an appropriate range of negative fluidic pressure must be maintained at the printhead nozzles, so that ink does not weep out of the printhead nozzles. The ink tank should be capable of containing the ink even under conditions where the pressure within the ink tank changes due to environmental conditions. For example, pressure variations within an ink tank can occur due to changes in ambient temperature such as when an ink tank is stored at elevated temperatures in a warehouse or a particular geographic region where high temperatures are encountered. Pressure variations within an ink tank can also occur when the ink tank is subjected to changes in barometric pressure such as transporting the ink tank in an airplane or a geographic elevation high above sea level. To this extent, most modern day inkjet ink tanks are designed with some means of pressure regulation to provide a suitable range of negative pressure to the printhead nozzles and to prevent loss of ink during substantial changes in temperature or pressure.
Various designs for regulating the pressure within an inkjet ink tank are known including, bubble generators, reverse bubblers, diaphragms, capillary media and bags. Each of these designs has limitations in the overall system performance of the tank. Ink tanks that use capillary media, such as a foam, fiber or felt, to store ink as a means for pressure regulation have the disadvantage that ink resides directly in the small passages of the capillaries. This is particularly problematic for pigmented inks since pigment particles having sizes greater than about 20 nanometers in diameter are subject to settling phenomena, for example, the pigment particles remaining lodged within pores or interstices of the capillary media. This is certainly the case for most modern day pigmented inks that have particle diameters in the range of 20 to 500 nanometers.
Pigmented ink can remain in an ink tank for several years from the time of manufacture through storage and use of the ink tank and this provides ample opportunity for the pigment particles to settle. Ink tank designs where ink is stored in capillary media leads to a situation where pigment particles are restricted in motion within the small passages of the capillary media. This restriction in particle movement is further complicated by the so-called Boycott Effect, wherein the observed sedimentation rate is increased in proportion to the available horizontal surface area within a capillary. For a more detailed description of the Boycott Effect see, Boycott, A. E., Nature, 104: 532, 1920. Both complications lead to an inhomogeneous distribution of pigment particles within the ink carrier fluid that can manifest itself as defective images during the printing process. For example, the non-homogeneous pigmented ink can result in images having a textured appearance reminiscent of a wood grain appearance if the pigmented ink is stored in the capillary media within an ink tank. This leads to a limitation in the selection of the pigment particle size since larger particles, which can be beneficial to providing higher optical density in printed regions, are disadvantaged from a settling and homogeneity standpoint when stored in a capillary media.
A second limitation for ink tanks using capillary media is the wasted ink associated with the capillary media. Ink tank designs where capillary media is used to store ink can result in a finite amount of ink that remains trapped in the capillary media at the end of the useful life of the tank. Ink that remains trapped is effectively wasted ink as it is not available for transport to the printhead and ultimately for printing of an image. It would be desirable to minimize the amount of ink trapped in the capillary media of an ink tank.
Ink tanks can be labor intensive and expensive to manufacture. In many ink tank designs, the lid of the ink tank must be tightly secured or bonded to the ink tank body after the insertion of the capillary media used for pressure regulation so that no ink leaks from the tank body. This can present a problem of properly aligning the capillary media during manufacturing of the ink tank and typically the capillary media must be inserted into the tank body prior to the bonding of the lid to the tank body. Prior art ink tank designs have the common feature that the capillary media resides between the ink tank body and the bond joint between the ink tank body and the ink tank lid. Furthermore, once the lid is bonded to the ink tank body (typically using a vibration or laser welding operation) it is impossible to remove the capillary media from the ink tank body without breaking the bond between the lid and the tank body or otherwise compromising the ink tank body itself. In most circumstances, this presents a major impediment to reuse of the ink tank since the ink tank can be damaged upon breaking the bond between the ink tank body and lid.
Refilling an ink tank with new ink once the initial ink is consumed may offer the potential for a cost savings since a new ink tank does not need to be manufactured. However, there are problems associated with refilling and reusing ink tanks where the initial ink in the tank has been consumed. For example, ink tank designs where ink is stored in capillary media results in contamination of the capillary media with the ink. In some cases, for example dye-based ink, it can be possible to refill the ink tank with the same colored ink provided that the initial ink retained in the capillary media does not adversely affect the newly filled ink. This is more problematic for pigment-based inks since ink trapped in the interstitials of the capillary media can flocculate and dry out as ink is consumed. Any ink refilled into an ink tank having the same starting capillary media would be contaminated with original pigment ink trapped in the capillary media. With both dye and pigment based inks, the ink tank would need to be re-filled with the same colored ink since any color contamination would greatly affect the performance of the ink. Even if it is possible to refill and reuse an ink tank, repeated refilling and reuse will successively degrade the printing performance, and particularly so for pigmented inks.
To this extent, it would be desirable to provide an ink tank that can be easily reused and refilled in a manner which permits the original capillary media in the ink tank to be replaced with a new capillary media without the need to compromise the structure of the ink tank body or bond joint between the ink tank body and ink tank lid. An ink tank design where the capillary media could be easily replaced, the ink tank easily flushed to remove original ink and the tank refilled with any color ink would be desirable. At present, ink tanks known in the art of ink jet printing do not achieve this desirable set of features.
Designs are known for ink tanks having a secondary ink storage chamber located within the main ink tank where the secondary ink storage chamber includes capillary media, such as U.S. Pat. Nos. 5,682,189, 5,703,633, 6,880,921, 7,252,378, and 7,290,871. Designs of this type suffer from the limitation that pigmented ink stored in the secondary ink chamber would be subject to settling and non-homogeneity during printing as discussed above. Designs of this type also have the limitation that the capillary media resides between the ink tank body and the bond joint between ink tank body and ink tank lid.
The limitations in the design of ink tanks for inkjet printers where capillary media is used indicates the need for an ink tank that would be capable of storing ink, even during conditions where pressure excursions can exist, where ink is not intended to be stored within the capillary media at normal operating pressures. There is also a need for a simple means of manufacturing an ink tank that contains capillary media as a means for pressure regulation. A need also exists for an ink tank which can be reused in a simple and effective manner.